Doublets, Coated Stones And Foilback

A doublet is a stone composed of two pieces cemented or fused together,
often of two different materials. The term triplet is sometimes applied
to that form of doublet in which the color is imparted to the stone
by the use of a colored cement to join the two parts, and also to a
stone consisting of three separate parts. The term foilback describes
substitutes made by affixing an opaque substance, usually a metal foil,
to the back of either a genuine or imitation gem material. Foil-backing
serves one of two purposes, or both: it increases reflection from the
back facets, thus making the stone appear more brilliant, or it imparts
color. The term assembled stone is sometimes used as the generic term
for any type of doublet, triplet or foilback. A coated stone is one
that acquires its color from an artificial, nonmetallic coating applied
to all or part of the stone.

The period of greatest importance for doublets and triplets was in
the era before inexpensive synthetic stones became available. At that
time, the most common doublet was that made by fusing glass to a garnet
crown and then polishing the stone. Since the advent of the synthetic
in quantity and in a wide variety of colors, the doublet's two major
uses have been as an inexpensive substitute for emerald and to lend
strength to a very thin piece of opal. The high price of synthetic emerald,
compared to synthetic corundum and spinel, has continued the need for
an inexpensive emerald substitute, since neither synthetic corundum
nor spinel is made in a satisfactory emerald color. The so called synthetic
birthstone rings are offered in such a low price range that the stones
used must cost well under $5 each.

Formerly, the various kinds of doublets and triplets were classified
on the basis of the nature of the material used in the composite, but
there seems to be little need for this. For example, a triplet consisting
of two pieces of colorless beryl with green cement to imitate emerald
was called a genuine doublet, the theory being that the composite was
made up of two pieces of the stone being imitated. However, the beryl
used is not emerald and the name is therefore a misnomer. Two pieces
of diamond joined to make a larger stone, or two piece s of opal joined
to make a more durable stone, are examples of genuine doublets. Such
names as semi genuine doublet, imitation doublet, false doublet and
others were used. It is felt that little is accomplished by such an
exhaustive classification. The present tendency is merely to identify
the parts, since there is little difference in value, for example, between
the parts of a beryl-and-beryl triplet and a quartz-and-quartz triplet.